1. Technical Field of the Invention
The present invention relates to a laser module, an illumination device, and a projection display device, and more particularly to an arrangement suitable in attaining high luminance using multiple laser light sources.
2. Disclosure of Related Art
In recent years, development of a projection display device (hereinafter, called as a “projector”) incorporated with a solid-state laser light source such as a semiconductor laser has progressed. A laser light source has an excellent performance in rendering a wide color space with high luminance and high precision, and has been noticed as a light emission source for a next-generation projector.
Despite the above demand, the laser light source has a large total heat generation amount, as compared with a lamp, and an output change with respect to a temperature change may easily occur. In view of this, in the case where a laser light source is used, improvement for cooling efficiency and strict temperature control are required. Heretofore, various methods for cooling a laser light source have been proposed. For instance, a laser light source may be cooled by using a heat sink, a Peltier element, or a liquid cooling system.
Also, as a demand for a large-sized screen has been increased in recent years, an increase in light amount has been demanded in an illumination device to be loaded in a projector. The light amount of an illumination device can be increased by arranging laser light sources two-dimensionally or three-dimensionally.
In the case where an edge-emitter semiconductor laser is used as a laser light source, the solid angle of output beam is significantly increased. In view of this, it is required to properly convert laser light into parallel light by a cylindrical lens or a like element to satisfactorily guide the laser light to an optical system (such as a fly-eye lens) provided posterior to the cylindrical lens or the like element. In the above arrangement, since a divergent angle of light in a direction of the longer axis of beam (hereinafter, called as “longer beam axis direction”) is large, it is necessary to convert laser light into parallel light at least in the longer beam axis direction.
In the case where an illumination device is constructed by arranging multiple laser light sources, the distance between the laser light sources may be increased in view of a point that a cooling part is mounted to the laser light sources as described above. Therefore, for instance, as shown in FIG. 2B, if illumination light is generated by converting laser light from each laser light source into parallel light by a cylindrical lens or a like element, the size of the generated illumination light may be significantly increased. As a result, an Etendue value of illumination light for incidence onto an optical system provided posterior to the cylindrical lens or the like element may be increased. The above arrangement may cause a drawback that satisfactory projection of illumination light onto an imager (such as a liquid crystal panel) is obstructed, and light use efficiency is lowered.